This invention relates to the determination of the existence and direction of incoming electromagnetic radiation, and, more particularly, to a body-worn system for pinpointing the source of such electromagnetic radiation.
For police work and, indeed, for military purposes, is oftentimes required that the source of an electromagnetic radiation be detected so that appropriate police or military action can take place. The electromagnetic radiation can come from as diverse sources as cell phones, military radios or any of a wide variety of transmitters, which, in general, are mobile, the location of which is important to the authorities.
For instance, in a border patrol scenario, when border patrol agents are seeking to locate individuals seeking to cross a border, if they are communicating with electromagnetic radiation, it is important to be able to find the direction of the sources, if not to pinpoint the source of the electromagnetic radiation, and, thereby, catch the invading border crossers.
Likewise, in a military situation, it is often required to be able to locate the source of a particular communications signal and to do so by direction finding means. In general, more accurate direction finding provides a bearing line indicating the direction of the enemy triangulation using multiple direction finders. It is also important for accuracy to be able to have a number of different direction finding units in the field so that through triangulation, the direction finding results from each of the units in the field as to the source can be pinpointed. The more direction finding units, the lower the area of uncertainty. The area of uncertainty, amongst other things, is dependent upon the number of direction finding fixes that are made.
While direction finding apparatus has been used in the past from fixed locations or mobile vehicles, it is important to be able to provide such signal detection and source location determination at each police officer or soldier assuming each of the police officers or troops could be provided with a simple direction finding apparatus, the operation of which is transparent to the individual as he or she carries out his or her duties.
There is therefore a need for the ability to detect where a communication is coming from to pinpoint the sources of electromagnetic radiation, and to do so in the manner that does not impede or impair other functions of the police officers or troops as they carry out their assigned duties. It is also a requirement that it not be necessary for the police officers or the troops to have any active partcipation in the detection of and location of the incoming electromagnetic signals. In short, it is a requirement that the system be a completely automatic so that nothing carried by the police officer or the soldier needs to be activated or in any way interacted with during the course of the maneuvers for which the system was intended.
In order to find a portable direction finding receiver so that the direction of a source can be ascertained or so that multiple direction fixes may be used to pinpoint its location of a source, in the subject system, a plurality of direction finding antennas are embedded into a wearable garment, with the multiple antennas being arranged such that a direction finding algorithm based on their outputs can be used to determine the direction of an incoming electromagnetic signal so that the line of bearing to the source of the signal can be ascertained.
Just providing the general direction is extremely useful so that an individual can quickly determine the direction of the source. This is done by computing a bearing line and indicating the bearing line direction to the individual. This can be done simply with a series of vibrators embedded about the garment and by activating the vibrator which lays closest to the bearing line. Thus, a soldier can get a quick indication of where the enemy is.
Having numbers of such bearing lines from different individuals results in the ability to pinpoint the source of the incoming electromagnetic signal by triangulation.
For border patrol scenarios, this means being able to quickly find the direction of an individual making a wireless call and with a number of bearing lines to locate the individual with sufficient accuracy that they can be apprehended.
In addition to the direction finding apparatus, which is body-worn, in one embodiment a transmitter is also located within the wearable garment so that the results of the direction finding procedure can be transmitted to a central location where through the receipt of numbers of bearing lines, the precise location of the source can be calculated. For this purpose, both a GPS receiver and a compass are required for each individual.
It is obviously important to be able to detected and locate electromagnetic signals over a wide variety of frequencies. Since the frequency of the electromagnetic radiation is unknown, it is important to be able to provide wide-bandwidth antennas capable of detecting radiation from frequencies of 2 MHz to 40 GHz.
One type of wide-band width antenna particularly well-suited for this application is the meander line loaded antenna described in U.S. Pat. No. 6,323,814 issued to John Apostolos and incorporated herein by reference.
This antenna, in general, is comprised of two parallel plates connected together through a meander line, one purpose of which is to minimize the overall size of the antenna. As described in the above referenced patent, the meander line provides a series of delays through phase discontinuities such that the effective length of the antenna is increased over that which the physical size of the elements would dictate. One of the plates is a ground plane. However, when body-worn, the ground plane would pass through the body of the individual wearing the antennas. In one embodiment at a corresponding series of meander line loaded antennas are provided on the back of the vest, with the combined action of antennas on the front and back of the vest forming a virtual ground plane which runs through the individual""s body where the real ground plane should go.
This means that effective broadband antennas can be brought down to a size that is wearable by an individual.
In one embodiment, as many as eight antennas are located on the body-worn garment, in one embodiment, a vest. An omni-directional mode is provided such that the presence of incoming electromagnetic radiation from any direction may be detected. The output pairs of antennas provide a so-called spigot, with omni-directional detection involving the spigots being fed in phase.
Once an incoming electromagnetic signal has been detected, direction finding analysis is conducted by sampling the spigots separately and proceeding with a correlation interferometric direction finding algorithm.
Knowing the geographical position and orientation of the antennas at any given moment in time through the utilization of a compass and a GPS receiver, the line of bearing from a precise point may be ascertained relative to magnetic north. With a number of transmissions of bearing lines from a number of locations to a central location the source of the electromagnetic radiation can be pinpointed.
The system is designed to operate whether the individual is standing upright or is lying on the ground, as would be the case during a military or border patrol operation. This is accomplished by processing the outputs of different pairs of antennas, whether the individual is standing up or is prone is determined by a sensor so that processing can be switched from the standing mode to the prone mode.
In one embodiment, the individual wearing the vest is unaware of the detection of incoming signals, or, in fact, the transmission of a bearing line, with the detection and direction finding being transparent to the individual as he or she goes about his or her duties. Alternatively, the individual can be immediately alerted as to the existence of a transmission and the direction it came from, i.e., xe2x80x9c30xc2x0 off to the right.xe2x80x9d The indication can be verbal with a synthetic voice or silent through lights or buzzers.
In operation, to pinpoint source location, a number of individuals are scattered about the countryside in an operation in which is it important to detect the existence of an incoming signal from a transmission and, also, the location of the source of the electromagnetic radiation. In one scenario, there may be as many as one hundred individuals wearing such wearable antennas and direction finding systems such that upon the occurrence of a transmission, the existence of the transmission and its line of bearing is ascertained by all of those individuals whose detectors are, in fact, detecting the transmission. There may be some individuals for whom detection is impossible due to various blockages or shielding. However, for the vast majority of these individuals in the area detection of the transmission is possible, along with determination of a bearing line through the use of direction finding techniques. The bearing line along with a position of the antennas and reference to magnetic north is transmitted to centralized location from each of the individuals and a precise determination is made through triangulation techniques. At that point, instructions can emanate from the central location as to how to take care of the source electromagnetic radiation, be it to go to the location and arrest the individual involved or to direct firepower to the location so as to eliminate the threat in a military sense.
It will be appreciated is that not only is the wearable antenna worthwhile in border patrol and military situations, for common police patrols where individuals are using cell phones for communication the detection of the transmission can make it infinitely easier to locate the individual, as he or she moves around the area. Not only are policing problems solved by the subject wearable system, the location of any kind of a offending transmissions such as an illegal transmission for which the Federal Communications Commission must act is within the scope of the subject invention. Thus, for instance, while it is usual for the Federal Communications Commission upon report of an illegal transmitter to send a vehicle with direction finding antennas on it, it is much more effective to send out a number of individuals wearing the subject body-worn system to more precisely locate the source of the offending radiation.
The subject system thus permits body-worn direction finding apparatus to be carried easily, with the results of the individual lines of position being usable to more accurately pinpoint sources of electromagnetic radiation. Whether used by police squads or by individuals, detecting and locating the source of a transmission is made easier through a body wearable series of antennas having wide-band width characteristics.
In summary, Body-worn antennas operate in combination with a direction finding processor to be able to detect the presence of electromagnetic radiation involved in communication as well as the direction of the source of the electromagnetic radiation. In one embodiment, a number of wide bandwidth antennas, 2 MHz to 40 GHz, are incorporated into a body-worn vest or garment such that an individual wearing the vest is being provided with a wearable system for indicating the direction of the source of incoming signals. If the orientation and geographic location of the individual are known via the use of a compass and/or by GPS receiver, the source of the radiation can be pinpointed by triangulation with inputs from other body-worn units. For omni-directional detection, pairs of antennas are provided with feed points or spigots which are fed in phase. Once an incoming source of electromagnetic radiation is detected, a direction finding analysis is conducted by sampling the spigots separately and proceeding with correlation interferometric direction finding. For troops in the field or police officers, the bearing of the source is most useful in knowing where the enemy or perpetrator is. In a preferred embodiment, each of the antennas is a meander line loaded antenna, in which the meander line loaded antennas are provided with a virtual ground plane passing through the body of the individual wearing the antennas. In order to provide the virtual ground plane, the antennas on the front of the vest provided are provided with corresponding duplicate meander line loaded antennas on the back of the vest. Meander line antennas are utilized due to their wide bandwidth performance, with the conductive plates in one embodiment being flexible conductive fabric. Depending on the processing of the outputs from the antennas on the vest or other garment, the system will work either with the individual in a standing mode or when the wearer is lying prone on the ground.